“Sleep disruption and ADHD are intertwined. Essentially, they are two sides of the same physiological and mental coin.”

Lack of sleep may be one of the root causes of Attention Deficit Hyperactivity Disorder, according to preliminary research presented at a pharmacology conference in Paris. In a small study of adults with ADHD, scientists found that those with the disorder had lower levels of melatonin around bedtime—a hormone linked to sleep—than average. The findings suggest that there may be a biochemical connection between ADHD and lack of sleep.

“If the connection is confirmed, it raises the intriguing question: does ADHD cause sleeplessness, or does sleeplessness cause ADHD?” said coauthor on the study Sandra Kooij of the VU University Medical Centre in Amsterdam, in a statement. “If the latter, then we may be able to treat some ADHD by non-pharmacological methods, such as changing light or sleep patterns, and prevent the negative impact of chronic sleep loss on health.”

The findings are not entirely surprising. Seventy-five percent of children and adults with ADHD also suffer from sleep disorders and scientists have long suspected that sleep disturbances are due to problems with the circadian cycle, mediated by melatonin. So the notion that ADHD and sleep disorders are linked by finicky melatonin and warped internal clocks is not farfetched. “A disturbance of the circadian system may indeed be a core mechanism in ADHD,” Andreas Reif of University Hospital Frankfurt (who was not involved in the study) confirmed in the statement.

After Kooji presented her key findings—melatonin and the normal sleep cycle kicked in about two hours late for the 50 adults in her study who had been diagnosed with ADHD—she went on to present a laundry list of evidence from prior research that has linked ADHD to delayed sleep. Core body temperatures associated with sleep tend to be delayed in ADHD patients, she said, and delayed sleep phase syndrome is particularly prevalent among those with ADHD. People with ADHD “simply cannot go to bed and fall asleep at the end of the day like others,” she said.

Kooji is careful to stress that her findings by no means prove that lack of sleep causes ADHD, or even that there’s a causal link between the two. Rather, she says, her research suggests that low melatonin levels and funky circadian rhythms may be one piece of the puzzle. “We don’t say that all ADHD problems are associated with these circadian patterns, but it looks increasingly likely that this is an important element,” she said. “Sleep disruption and ADHD are intertwined. Essentially, they are two sides of the same physiological and mental coin.”